(Adapted from applicant's abstract): The goal of the research proposed is to further understanding of the mechanisms of membrane traffic. The work will concentrate on the TAP (transcytosis associated protein complex, a recently identified complex of proteins required for fusion of specific membrane partners, but not required for all fusion events. The complex is specifically associated with transcytotic carrier vesicles (TCVs) and is necessary for their fusion with the apical plasma membrane (PM). The data suggests that the complex is involved in membrane recognition events. Currently, only small GTP-binding proteins are known to participate in membrane sorting, and consequently, defining other components that influence this process is of great significance for the elucidation of the mechanisms mediating membrane specificity. Dr. Sztul plans to characterize the subunit structure of the TAP complex and to define the function of distinct subunits. She will analyze the requirements for assembly of functional TAP complex and study the mechanism of its specific attachment to the TCV membrane. She will also analyze the morphology of the complex and correlate distinct functional domains with morphologically defined structures. The function of the complex will be assessed in a modified assay in which targeting and binding can be separated from later stages of fusion. Using the system, interactions of the TAP complex with other molecules known to influence vesicular traffic will be examined. Most of the functional analyses will utilize biochemical and morphological approaches while the characterization of distinct components will use molecular and genetic procedures.